Plant Selection, Installation, and Management to Affect Groundwater - Introduction to Phytoremediation of Contaminated Groundwater - page 162

in arid areas of the western United States, although some
also are present in the more humid East. One plant, the
saltcedar, was not recognized in the early work of Meinzer
(1927), because although present, it had not yet begun to
invade the southwestern United States. Therefore, this
supports conclusions that saltcedar probably was imported
from the Mediterranean area into the United States sometime
before 1927.
Another phreatophyte found in arid areas of western
North America is the rabbitbrush ( Chrysothamnus spp. ).
Although it can be found growing in areas where the depth
to water table is deep, a thriving stand indicates a shallow
water table between 8 and 12 ft (2.4-3.6 m). White (1932)
first observed that it uses groundwater when he stated that
wells installed in areas where rabbitbrush grew had a daily
fluctuation in the groundwater level. Interestingly, these
plants contain about a 6% non-latex rubber content of
chrysil, which may serve defensive purposes or provide a
way to store excess photosynthate for later use.
Other native phreatophytes that use groundwater but are
more important in that they can indicate groundwater of
poor quality include pickleweed. Pickleweed ( Allenrolfea
occidentalis ) is a succulent shrub characterized by very
small leaves and can grow where the salt content of soils
and groundwater is high. For example, the soil where pick-
leweed grows usually contains about 1% salt. Plant-tissue
samples from pickleweed growing near Malad Valley, ID,
indicate that the sodium and chloride content of pickleweed
can be as high as 26 mg/g (mg per gram; Robinson 1958).
At Death Valley, CA, Robinson measured groundwater
concentrations of sodium and chloride where pickleweed

was growing and observed a conductivity of 31,600 mho

(micromhos) and a chloride content of 12,800 ppm (parts per
million; Robinson 1958). While the presence of pickleweed
may be used to indicate shallow depth to water table, the
quality of the groundwater may render it unfit for irrigation
or potable use.
The common rose also uses groundwater in its native
habitats. Meinzer (1927) observed several roses growing at
a spring mound near Big Smoky Valley, an otherwise arid
area. Also, the 190-year-old Lady Banksia rose growing in
Tombstone, AZ, must have as its source of water deep
groundwater (Fig. 7.2 ).
Native palm trees also tend to be phreatophytes. The
Washington Palm, for example, the only palm native to
the United States, has a shallow root system but can survive
in otherwise desert conditions because of their location near
springs. This relation between palms and groundwater is the
reason behind desert oases as described in Chap. 1. Unlike
other arid groundwater plants, these palms can reach heights
greater than 50 ft (15.2 m) and are used by weary travelers to
guide them to oases of shade and cool water. Trees that can
be classified as phreatophytes and found in the more humid
eastern United States include birch, such as river birch
( Betula nigra ), sycamore, alder, walnut, and various oaks
(Table 7.3 ).
An evergreen plant that may be useful in phyto-
remediation applications because of its moderate growth
rate, survival in moist soils, and evergreen habit is the
Eastern red cedar ( Juniperus virginiana ). Contrary to its
common name, the Eastern red cedar is not a true cedar, or
Cedrus . This tree is found throughout most of the eastern

m

Fig. 7.2 This enormous 190-
year-old Lady Banksia rose grows
in a courtyard in Tombstone, AZ,
and is as popular a tourist
attraction as the nearby OK
Corral. In this arid area, the
longevity of this plant is
attributed to its use of deep
groundwater (Photograph by
author).